A household sauna is generally provided with a sauna chamber of a size to permit usually one person to enter, the chamber having side walls, a front wall, a back wall and an upper ceiling or cover, and electric heaters such as on the front wall and the back wall to heat the interior of the chamber. Sauna apparatus of this type elevates the interior temperature of the sauna to 60.degree. C. or higher, such as to promote perspiration of the user of the sauna. However, for elderly or sick persons the physical load imposed by such higher sauna temperature can become sufficiently great to present a danger. Sauna apparatus was proposed for such situations, in which the temperature in the sauna chamber can be set a lower temperature, e.g. about 40.degree. C. which will not cause perspiration, but will promote blood circulation of the user by the so-called thermal effect at a lower temperature, such as in a warm bath.
When the sauna is to be used at normal high temperatures suitable to produce perspiration with conventional control system, even if the temperature is set only for warm bath type use for example at 40.degree. C., the temperature in the sauna chamber can significantly fluctuate about the set temperature making it difficult for comfortable use. Therefore, a special control unit has to be employed which will make the cost of the sauna apparatus high.